textproduct: Rapid City

KEY MESSAGES

- Southwest flow aloft expected through the weekend, which will bring temperatures 5-10F above normal on average.

- Upper trough moves through for early next week bringing increasing precipitation chances Sunday night through Tuesday.

UPDATE

Issued at 1038 PM MDT Thu Sep 24 2026

Expanded coverage of at least patchy fog across our South Dakota plains east of Rapid City late tonight into Friday morning, and introduced some light PoPs for a few showers and thunderstorms tomorrow afternoon/evening in northeast Wyoming south of Gillette into far southwestern South Dakota. Otherwise no major changes needed. Still looking ahead to Sunday night for the bigger trough and significant increase in the chance of rain and storms.

DISCUSSION

(This Evening Through Thursday) Issued at 130 PM MDT Thu Sep 24 2026

19z surface analysis had remnants of warm front from the eastern Dakotas into eastern CO, which has left the CWA dry as the focus for precipitation has shifted well southeast of the CWA. Plenty of sunshine over the CWA as shortwave ridging pokes into the northern Plains per water vapour loop.

Tonight/Friday, shortwave over the southwest CONUS will race northeast and gently brush the southeastern reaches of the CWA with low PoPs. Southeasterly boundary layer flow later tonight/early Friday will support fog/low clouds east of the Black Hills. Latest ensemble guidance continues the trend of yesterday with further east movement for this wave, so confidence high most of the CWA will be dry Friday. Fly in ointment may be over the far southwest where a sliver of weak buoyancy suggests unmentionable PoPs at this time with CAM support minimal. Temperatures will be near guidance.

For the weekend, southwest flow aloft and thermal ridge will support high temperatures 5-10F above normal along with dry weather given little moisture availability. An upper trough will approach the northern Plains Sunday night through Tuesday with modest moisture return and sufficient forcing for good chances of shra/TS. Machine learning guidance suggests potential for some active/strong storms Sunday night/Monday. Temperatures will become seasonal as associated cold front passes through. Long range guidance suggests zonal, mostly dry flow with slightly above normal temperatures.

AVIATION

(For the 12Z TAFS Through 12Z Saturday Morning) Issued At 544 AM MDT Fri Sep 25 2026

VFR conditions are generally expected through most of the TAF period, at least for our TAF sites.

Low stratus and fog have developed across parts of the South Dakota plains on the eastern edge of the CWA. For now, the fog looks to fade out between 15-17z/9-11am MDT. IFR/LIFR conditions will be possible in these areas. Still not thinking the fog and stratus will reach as far west as KRAP, but it might be close...the probability of impacts drifting into the terminal is currently 20-30%.

Otherwise, only high-level clouds and dry conditions are expected, with breezy southeast to south winds starting tonight at KGCC and continuing through the forecast period.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until 11 AM CDT this morning for SDZ046-047- 049. WY...None.